From Synthesis to Failure: In Situ Characterization of Lithium-Ion Battery Cathodes.

Developing high-performance, long-life lithium-ion batteries requires an in-depth understanding of cathode material synthesis, lithium-ion (de)intercalation mechanisms, and structural failure processes. Traditional ex situ characterization techniques, however, capture only static snapshots and often introduce artifacts by disrupting the material's original state. In contrast, advanced in situ characterization techniques enable real-time, non-destructive monitoring of dynamic evolution in crystal structure, morphology, and chemical states under operating conditions. This review systematically summarizes the principles and recent progress of key in situ techniques-including X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, neutron diffraction, nuclear magnetic resonance, transmission electron microscopy, electrochemical impedance spectroscopy, Raman spectroscopy, infrared spectroscopy, electron paramagnetic resonance, and differential electrochemical mass spectrometry. We analyze their applications across three critical aspects: cathode material synthesis, lithium-ion deintercalation mechanisms, and failure mechanisms. Furthermore, we discuss emerging strategies of multi-technique integration and artificial intelligence (AI)-assisted data analysis, which offer transformative potential for deciphering complex physicochemical processes. This multi-technique collaborative paradigm provides new insights and pathways for overcoming current performance bottlenecks and accelerating the development of high-energy, long-life lithium-ion battery cathodes.